Scribing arcs and circles upon work pieces, such as sheet material and the like by accurate means, has been a problem confronting machinists and other types of metal workers and the like for many years. Related to the problem is the cutting of discs or flat annular type of devices or items formed from various types of material, including metal. The cutting of curved surfaces on glass also presents related problems.
In attempts to solve some of these problems, tools comprising a central pivot adapted to be placed stationarily upon a sheet of material to be cut and provided with an arm having one end connected to the pivot and the opposite end having a cutting tool of some sort thereon are disclosed in the following patents, which are representative of this type of tool:
______________________________________ U.S. Pat. No. 520,247 Sinsz May 22, 1894 U.S. Pat. No. 1,791,648 Tate Feb. 10, 1931 U.S. Pat. No. 2,269,510 Bates Jan. 13, 1942 U.S. Pat. No. 4,044,464 Schiess et al Aug. 30, 1977 ______________________________________
The cutting of circular holes also heretofore has employed tools similar to the foregoing with the exception that a scriber has been included on the horizontal bar in addition to the cutter and such a device is the subject matter of prior U.S. Pat. No. 2,795,277 to Wortham, dated June 11, 1957.
A cutting tool operable about a vertical axis and having a horizontal arm which supports a pair of cutters also has been devised heretofore and is the subject of prior U.S. Pat. No. 2,546,292 to Bell, dated Mar. 27, 1951.
For drafting purposes, instruments known as beam compasses have been employed for many years, some of which even include the feature of adding extensions to the horizontal bar upon which the drafting marker is carried with respect to a stationary pivot placed in the drawing. A typical device of this type is illustrated in prior U.S. Pat. No. 2,512,235 to Lankford, dated June 20, 1950.
The foregoing patents are merely illustrative and exemplary of a very substantial number of tools for making circular cuts, scribing or drawing circular lines and the like. For machine work, however, it is frequently necessary to be extremely accurate with respect to the arc or circle to be drawn upon a work piece, and on occasions, even the matter of a few thousandths of an inch is critical. To determine the radius length to such precise dimensions, resort to the use of accurate gauge blocks of well-known machine type is required, and the present invention provides a scribing tool with which gauge blocks readily may be employed to determine the desired radii of a very precise nature. The structures shown in the prior U.S. patents referred to above have no such means for utilizing gauge blocks to arrive at a desired very precise radius of either a cutting or drafting tool.